Lockup for printing presses



Feb. 9, 1954 L, MQWHORTER 2,668,497

LOOKUP FOR PRINTING PRESSES Filed Feb. 7, 1950 2 Sheets-Sheet l pag.. z

TTORN E;

Feb. 9, 1954 H McwHoRTx-:R 2,668,497

Lookup FOR PRxNTING PRESSES Filed Feb. 7, 195o -2 Sheets-Sheet 2 LEADINGEDGE CLAMP Figs 62 LEADING EDGE CLAMP TRN LING EDGE. CLAMP III-"558 ma,wy-

anyway patee close toeoneanother for tiles-pri Patented Feb. 9, 1954patle of letame@ bending in respon-Se to arose i 2" Y Wastagje or paperbut also in an considerable sacinthe capacity of' the press'- iraddition to cumpli-eating theV pressrnanis; layoutI Work; Be# cause' oflthe invv'ardyVv direeted force; the plates ar'e likely to loe'f'comevprogressively peenedat the' regional of oontaot With tl'ie olaxriasvil-rienA creasestlie likellio'od' that a' plateiwill be-tlrown bycentrifugalfforoes':

M'l'lcir effort has' been' expended inarr endeavor tc ove'reoinetlre'se` inherent disadvantaged and patent appiications have been led onvarious iodieations'- of' the C'laybournlocieuizrintended? aslimproveinents'. An'L example is to' kie-'fourmiJ tliey lue'hrs Patentm4665883 issuedi on? Sep`l texnber' 3;- 19461. While offering*considerable promiseVA from a`- pu'r'el'y theertieal standpoint; sicli'`arrangements hate s'u-redi from serions' herent disadvantages. First orallA there isi an assumption tliatthe' plates Wil-lretain` theiroriginai dnfrengiijrf after heir-ig draw-rr tight on the eylinder'`rnerelyleeau'se they are clamped iin ten-- sion. My experiencehasshowni' that' th'ei plates tend to' Worl loose, ffronil aisiin'fpletension liinlup and@ the lla-rese r'riust 16e' shut down# at'vfrequent iritertal tof take upl on` the adjfus'trrient,E partita# larlyin the peripheral direction. It is often neef-Y essaryJ to* reregistervtl'iie isx done; Even more-yi( portantftle number of-eiear impressionsWhelmay k)"`e"'r1'a.d"e'S bly a'eh-Zof; the" platee is? Iiinte'cf rld:Lthe lil-'Elites themselves@ tendi toi bei deh stroyed by the fatiguewhicnoeciir's. as afre'sult of'L repeatedL rollingirpaetthe impressioncylinder. A further disadvant ge of the* reeent prior#` art arranenints"has! tof do: with the time 1q'fued'k t insert" he make'ifetdy to; eiect:ain even printing impression. After an initiaiioi'trial nuritin-necessary te unrastenf the plate cramps attneftrailing edge btalsoithose along the sideso'f the'plat'e Titisi's'fnotf-onlt'f' alerit'hyprocediire because' of# tliel largei of elan-ips Which are involved inthe securing; of ai sirigrl'e plate,I aiSOf tends-f tof d'st'lf'o'y theregisteradjustmemalv sei matth'e 'plate mastn be reufegisterd after" themakeread procediniei hasy fnallyf been completed:

c'rdirigly it is? an btci` ofV the Irwell-tio 110 provide a tensionrloc'kupfoi" magazine? pr ing plates WI-i-ieh pernfilitsY a? much-fgifefftei'-- preduotion of clear"risteredflinipressions thanfa'i'lyavailable prior ard-lookup.Withotatigu or daiagetethe plates and withoutnecessity for snuttiiig'ddwnfbr elfe' hgfpribdtlellp @t-iiimpsor 0"resto'r t jeet preti-ide an improv-edf' tehsion leolli the tendran @fr agfiiien platea-midi careful initial adjustment and in which the tensionunder operating conditions is automatically and continuously adjusted tothe minimum value required to seat the plate securely and safely. It isa related object to provide a tension lookup of the above type in whichtakeup at the trailing edges of the plate occurs automatically tocounteract any circumferential elongation which may occur eitherinitially as a result of conforming the plate to the cylinder or whichmay occur under running conditions.

It is a further object to provide an improved tension lookup for amagazine printing plate in which the register adjustment may beprecisely maintained even where it is necessary to remove the platerepeatedly for the addition of makeready. It is a correlative object toprovide means for easily and quickly obtaining axial register and formaintaining it by relatively light clamping pressure in the axialdirection.

It is still another object to provide a tension type lookup which iscapable of locking the plate into position automatically upon slowrotation of the printing cylinder incident to installation of additionalplates and in which the locking force increases in step with thecentrifugal force which tends to throw the plate outwardly.

It is a still further object to provide an improved tension lookup whichis applicable to magazine presses of conventional design and whichpermits of cylinder rotation in either the forward or reversedirections. It is a more detailed object to provide a lookup arrangementwhich is inexpensive to manufacture and which may be applied to existingplate cylinders without the necessity of making any change whatsoevertherein and with only minor modification of the printing plates.

Other objects and advantages of the invention will become apparent by areading of the following detailed description and reference to thedrawings, in which:

Figure l is a schematic representation of an impression cylinder havinga plurality of plate cylinders to which the present invention isapplicable.

Fig. 2 shows a printing plate of the type preferably utilized inpracticing the invention.

Fig. 3 is a fragmentary plan view showing the adjacent corners of fourprinting plates secured to a plate cylinder.

Fig. 4 is a sectional view of the plate cylinder taken along the line4--4 of Fig. 3.

Fig. 5 is a general perspective of one of the leading edge clampsemployed in the present invention.

Fig. 6 is a cross section of one of the leading edge clamps taken alongthe line 6-6 of Fig. 3.

Fig. 7 is a general perspective of one of the trailing edge clampsforming a part of the present invention.

Fig. 8 is a cross section of a trailing edge clamp taken along the line8-8 of Fig. 3.

Fig. 9 is an enlarged fragment of one of the trailing edge clampsillustrating the function of the sliding weights and showing the angularrelationships employed therein.

Fig. 10 is a general perspective of a side clamp forming a part of thepresent invention.

Fig. 11 is a cross section taken along the line H-ll of Fig. 3.

While the invention is susceptible of various modications andalternative constructions, I

have shown in the drawings and will herein describe in detail only thepreferred embodiment; it

is to be understood, however, that I do not thereby intend to limit theinvention to the specific form disclosed, but aim to cover allmodifications and alternative constructions and uses falling within thespirit and scope of the invention as expressed in the appended claims.

Turning now to the drawings, Figure l shows a portion of a magazinepress including an impression cylinder 29 and plate cylinders 2&-25distributed about the periphery. Each one of the plate cylinders issupplied with ink of a different color by suitable inking mechanism (notshown) for color printing of a web 26.

Fig. 2 illustrates a plate 3B of one type which may be employed in thepresent invention. This plate includes undercut grooves 3l, 32 whichextend uninterruptedly along the leading and trailing edges 33, 3drespectively of the plate. The plate is comprised in the conventionalmanner of a light electrically deposited shell which is plated with ahard wear-resisting metal to form a printing surface. The shell is thenbacked with a soft lead alloy to a total thickness of approximatelyone-quarter inch, the alloy being sufficiently deformable so that anaccurate impression level can be established by raising low areas withsmall shims of paper or makeready- The manner in which the makeready isapplied to the underside of the plate is indicated at 35. For a reasonwhich will later appear the side edges 40, 4l of the plate are madesquare with respect to the surface of the cylinder. A plurality of suchplates are arranged substantially edge to edge on the plate cylinder 2las shown in Fig. 3. Portions cf four plates are shown, correspondingparts of each of the additional plates carrying subscripts c, b, and crespectively.

The plate cylinder 2| is of a conventional type employed in magazinepresses. As illustrated in Fig. 3 and in the cross section of Fig. 4,evenly spaced helical grooves 5G are machined in the outer surface. Acontinuous rack 5| is provided at the -bottom of each of the grooves,such rack being normally engaged by suitable pinions included in theclamps employed for securing the plates. The side walls 52, 53 of thegrooves are provided with narrow undercut locking grooves 54, 55. Theseare arranged opposite one another and are bridged by a suitable lockingbar in each of the clamps to prevent outward displacement.

In accordance with the present invention a tension lookup is providedcomprising means for anchoring the forward end of the plate togetherwith an improved non-retrograde followup device for positively anchoringthe trailing edge of the plate and without applying any undue stressthereto. Further, in accordance with the invention, side clamps areprovided for engaging the squared edges of the plates for preventingaxial displacement while permitting removal of the plate for purposes ofadjusting the makeready.

Attention will first be given to one of the leading edge clampsindicated at 60 in Fig. 5 which hasa body 6l which is formed of twoshell-like halves Sla, Blb held together by suitable cross screws 63.The body of the clamp is dimensioned to rlt Within one of the grooves 50and carries at one end a hook 62 for engaging the undercut groove in theleading edge of the plate. Y As set forth in detail in the cross sectionof Fig. 6, the leading edge clamp is propelled along the groove by meansof a pinion 'l0 engaging the rack 5l. The pinion is turned by a worm 'Hwhich is` enapplied to the cylinder.

'gaged by a suitable wrench t! fitted into an upwardly facing socket 12.Because of kthe .me-

chanical advantage provided by the worm the wrench maybe of very lightconstruction and, since the worm provides an irreversible drive, theclamp is automatically locked in position relative to the rack.

.For the purpose of maintaining the clamp seated firmly within thegroove a double winged lock 'l5 is provided which is .rotated into thebridging or locked position illustrated in Fig. 5 by a suitable wrenchinserted 1in the socket le formed centrally therein. A detent 80 isprovided .in order to signify to the operator by feel that the lock isengaged with the registering grooves. As one of the more .detailedfeatures of the lead- ;ing edge clamp, the hook t2, which is mounted forswlveling in the `clamp body, is also provided with a detent indicatedyat 8|.. This detent .is so arranged that with the .clamp normally.seated in -one of the helical grooves the laterally .extending portionsof the hook 82 will be properly oriented to engage the groove in theleading edge of the plate. This is vof advantage since a large number ofclamps of the type illustrated `are normally employed arranged side byside with all of the hooks in general alinement before the rplate may beAs shown in Fig. 3 a leading edge clamp maybe used in each of thesuccessive grooves.

Turning .next to the trailing edge clamp disclosed in Figs. 7., 8 and 9it will be noted that the appearance is somewhat .similar to `theleading edge clamp. Thus, the clamp indicated at 90 includes a body 9|having .opposed halves Sla, tlb held together iby cross .screws 92. Theclamp is adjusted along the groove by a pinion |08 driven by a Worm IUIrotated `by .a .manually operated wrench inserted at |02. A doublewinged lock |05 may be rotated around into loc-king lposition by meansof a Wrench inserted in a socket |06. A

plurality of such clamps are used in the successive grooves along thetrailing edge of each of the y plates as illustrated in Fig. 3 with thesuccessive p clamps each designated by the numeral y9 0,.

For the purpose of engaging the trailing end of the plate in tension ahook I is used which `is not freely rotatable as in the clamp previously`described but has `only limited play so that the hooks of vsuccessiveclamps are maintained .generally in line with one another. In practicingthe invention the hook I0 has a limited range of hooking movement and isbiased in the plate clamping direction. In the present instance this isaccomplished by mounting the hook ||0 on a pivot nger and by arranging alight leaf spring |2 -so that it presses against the finger. Pivoting isaccomplished by providing a shaft-like enlarge- 1 ment at the lower endof the finger as indicated .at I3 in Fig. 9 and by forming a suitablereceptacle or groove I |4 in the body :of the clamp. .As

; shown in Fig. 9 the back side of theleaf spring |2 presses against thebody of the clamp to urge the hook .in the clockwise or :clampingdirection. The pressure is such as to overcome :all frictional Vforceswithin the clamp but `not so great as to have any noticeable tensioningeffect on the plate.

Means are 4further provided Vfor .locking the hook against .retrogrademovement iin response to the action of centrifugal force on a weightwhich is l freely movable in the clamp body. In the embodinientillustrated inFigs. '7, 8 and .9 va weight indicated at |120 isslida'ble in a bore |121 which ex- .ten'dsradially lwith respect Vto theplate cylinder;

A manually al-ined. '75A when the clamp'is in operating position. 'Thelocking eiect is obtained `by providing a nonreversible wedging surfacebetween the weight and the vhook H0 for maintaining .the hook wedged inthe clamping or clockwise position to which it is moved by the spring||2. In the present instance this is accomplished by a wedge vblock |25which is integrally formed on the finger member l and which has awedging surface I 26 which ydirectly engages :the weight. Preferably theweight is chamfered .at its upper end to increase the bearing areapresented to the wedge block. While the wedge angle indicated at fAshould be shallow so as to block the finger member I from backing upunder the tensile forces in the plate, the actual value is not critical.As a matter of fact the effect of wedge angle will change from arelatively high value which exists when the weight |20 is inthe lowposition illus- `trated in Fig. 8 to a minimum value `when the weight isin its maximum outward position which -is approached in Fig. 9.Preferably the effective Wedge angle should be less than 30 degrees overthe'useful range of movement of the weight although the nature of ythesurfaces at the vpoint of engagement will affect Vthis somewhat with asmooth surface requiring a shallowcr angle. Any stickinessor corrosionwhich may develop makes it diiiicult for return or inward movement ofthe weight to occur and will merely have the effect of 'increasing thepositiveness of locking.

While the weight maybe of -any desired high density metal havingappropriate resistance against Wear, I prefer to :employ apellet ofsintered tungsten since this material has a density which Aisconsiderably greater than that of lead. In this way the rotation of the:printing .cylinder will cause the Weight |20 to Ifly yforcibly .outwardinto its locking position, thereby overcoming any tendency for theWeight to stick in the innermost position illustra-ted in Fig. 8.Since'the effective locking force varies directly with the .centrifugalforce and, consequently, ywith :the speed of :the plate cylinder, suchforce will be at all times in step with the centrifugal force tending tothrow the plate outwardly. While the locking force exerted by the weightvaries with the speed n.of

rotation it is to be Vespecially noted ythat 'locking is positive andreturn movement of the plate is prevented at all speeds even down tostandstill.

Preparatory to any detailed outlining of the operation of the tensionlookup thus far ...described, reference Awill be-made to the side clampdisclosed in Figs. 10 .and 11 a number .of which `serve to 'position theplate for axial register. An exemplary clamp indicated at i|3 has a body:|3| consi-sting of two halves lilla, l`3lb. Included within the clampis a double winged lock .1.32 having wings |33, |34 and .a '1T-shaped.abutment |35. The latter has a smooth ysubstantially :at `face forengaging the square edges om or 419 of the plate and for permitting the`plate :to .be withdrawn radially away from the plate cylinder withoutA.disturbing the axial'register adjustment.

Preferably :the abutment |35 is .alned with the locking wings |33, |34and is lconstructed :integrally therewith so `that `when the side clampis in the position illustrated in Fig. 3 the Wings will -be positionedin the locking grooves 54, 55. A detent |36 is provided so that with theside clamp in position the abutment automatically assumes `a-positionalined lwith 'the edge lof the plate :mak-

ing it `unnecessary for veach of the clamps to be As in fthe case vofthe yprevious clamps, means Vfrom the undercut portion of the plate.

are provided for adjusting the clamp in its groove. This function isaccomplished by a rack pinion and a worm |4| both of which are suitablyjournaled in the clamp body. In accordance with one of the more detailedfeatures of the invention the worm |4| is made accessible through theabutment |35. A wrench may be used for this purpose, extending through abore |42 in the abutment and engaging the socket |43 in the worm. Itwill be apparent from Fig. 3 that this makes it unnecessary to provide aseparate opening in the body for adjusting the clamp and makes itpossible to space the adjacent printing plates practically edge to edge.

Rsum of operation In operation leading and trailing edge clamps 6l), 90are mounted in the plate cylinder in the manner disclosed in Fig. 3 andwith the hooks respectively engaging the groove 3| at the leading edgeand groove 32 at the trailing edge of a given plate. Side clamps |39 maybe positioned at the end portions of the plate or, if desired, atfrequent intervals along the sides of the plate, for example in everysecond groove. The adjusting pinions in the leading edge clamps and sideclamps are then adjusted by suitable square head wrenches until acondition of at least approximate register is secured. After this thetrailing edge clamps are retracted in their grooves and relative to theedge of the plate until slight resistance is encountered. This indicatesto the operator that the hooks bottomedf in other words, have swung themaximum distance counterclockwise as viewed in Fig. 9. The operator thenstops turning the wrench since forceful turning would cause the hooktobreak. The resistance encountered not only signifies to the operatorthat the clamp is properly adjusted but insures that the full range ofhook movement,

preferably on the order of an eighth of an inch, is available to take upelongation of the plate.

At this time the weights |2 in the respective clamps will be in thelowered or at-rest position disclosed in Fig. 8. As the plate is rotatedaround to the bottom of the cylinder for installation of additionalplates, the weight |20 will, of its own accord, fall into the lockingposition shown in Fig. 9. Because of the undercutting of the groove 32and the corresponding angling of the face of the hook, the plate will beeffectively locked on the plate cylinder. Upon bringing the plate up tospeed, centrifugal force causes the weights to have a forceful wedgingeffect. A trial run can then be made in order to test the evenness ofimpression and to check the condition of register.

Final register adjustments may be made at the leading and side edges ofthe plate.

To remove the plate for addition of makeready it is merely necessary toinsert a wrench into the trailing edge clamps to cause the clamps towalk along. their grooves until the hook is disengagd T e weights willdrop free, whereupon the plate may be lifted off, the makereadyinstalled, and the plate reapplied to the cylinder all withoutdisturbing the register adjustment. The trailing edge clamps are againadvanced to the operative position so that the cylinder may be rotated.As before, the first rotation will serve to cause the weights to fallinto position so that the plate is immediately locked after whichautomatic takeup will occur exactly in step with elongation of the plateregardless of the reason for such elongation.

It will beapparent that the automatic takeup 8 feature with itsnon-retrograde action produces an eifect which may be clearlydistinguished from tension lookups of the positive type and also fromtension lockups in which resilient spring pressures of large magnitudeis depended upon to secure the plate. It is a well known fact that theinitial seating of the printing plate which occurs during the rst fewrevolutions causes the plate to elongate. Normally it would be necessaryto stop the press in order to compensate for such elongation. In thecase of the present device, however. this initial elongation is taken upautomatically as it occurs. It is to be further noted that the pressureexerted on the plate is at all times that which is required to hold theplate in position and is independent of any decision or judgment on thepart of the operator. All it is necessary for the operator to do is toposition the trailing edge clamp so that the spring is eiective to forcethe hook into contact with the undercut edge of the plate. The spring ispurposely made very weak so that it does not substantially contribute toholding the plate in place. On the contrary the holding eifectis duealmost exclusively to the `ifleding engagement of the Weight and thewedge Practical tests made employing clamps as shown and describedmeasuring only 1%" in Width and not exceeding 1%" in length show thatplates may be securely anchored to a 35- inch circumference platecylinder at speeds of 1,000 R. P. M., more than three times the usuallyattained speed of plate cylinders in high speed magazine presses ofmodern design. Speeds higher than 700 R. P. M. may be maintained forextended periods without any signs of weakening and without necessity.for. touching any of the clamping adjustments.

My investigations, which were made in an endeavor to explain thesurprising and disproportionate results which have been achieved,indicate that the positive holding force developed at the trailing edgeclamps is established as an incident to the rolling out of the printingplate on the plate cylinder by the impression cylinder. As theimpression cylinder is rolled progressively along the plate cylinder twothings occur. In the rst place there is a slight elastic elongation ofthe plate which is progressive and which reaches a maximum when theimpression cylinder is about to leave the trailing edge of the plate.Secondly, there is a relieving of the stress exerted by the plateagainst the hooks at the trailing edge. Then, as the impression cylinderleaves the plate there is a tendency for the plate to contract to itsoriginal dimension and to reestablish the stress. In tension lookups ofthe conventional type the cyclical stretching and contracting whichoccurs at each revolution and the changes in stress which accompany itconstitute a working of the pla-te which not only accounts for the wearon the printing surfaces but also results in fatigue of the crystallinestructure with the risk of throwing a plate at high speed or afterextended periods of operation. In the present construction, it is true,a certain amount of plate elongation occurs. However, -because of theimmediate follow-up action at the wedging surface, the hooks in thetrailing edge of the plate will be repositioned and locked positively inthe new position because of the nonretrograde feature. As a result whenthe impression cylinder leaves the plate cylinder the latter cannot snapback to its original dimension. In spite of cyclical variation in theforce 9 exerted by the plate against the hooks at the trailing edge,fatigue due to repeated straining is substantially eliminated. It isfound that the tension in the hooks varies automatically to keep theplate firmly seated on the cylinder and there is no possibility ofoverstressing the plate due to application of excessive initial clampingpressures. A stable operating condition is established after the rst fewrevolutions and it is unnecessary to stop the press even during thecourse of long runs to restore register or to make a takeup adjustment.

One of the important results brought about by the present arrangement isthat the complete lack of working serves to substantially reduce thewear on the printing areas. Tests have shown that 2,000,000 impressionsmay be made by a plate employing the new lookup without any substantialwear, while plates employing more conventional lockups are useless afterrunning approximately 1,000,000 impressions and, under certainconditions, considerably less.

It will be apparent to one skilled in the art that the present improvedlookup is applicable to presses now in operation merely by millingundercut grooves along the leading and trailing edges of the plates andby squaring off the sides. The mechanical elements comprising the clampsare simple and straightforward permitting economical assenbly and greatstrength even in the small sizes in which the clamps must be constructedto t in the conventional grooves. Be-

cause of the extremely small access requirements,

the plates may be arranged ahnost edge to edge in both directions andtheprinting of bleeds in any and all positions with little waste becomesfeasible.

I claim as my invention:

1. In a tension lookup for clamping a printing plate on a printingcylinder, the combination comprising, a leading edge clamp for engagingthe leading edge of the plate and positioning the same for peripheralregister, a trailing edge clamp having a hook for engaging the trailingedge of the plate, said hook being movable in said clamp, a weightradially movable in said trailing edge clamp under the influence ofcentrifugal force, and means including a wedging surface between saidweight and said hook for urging the hook in a plate tensioning directionupon outward movement of the weight, the angle of said wedging surfacebeing sufficiently shallow to prevent retrograde action whereby theplate is maintained at a constant peripheral dimension so that cyclicalworking of the plate on the cylinder is obviated.

2. In a tension lookup for clamping a printing plate on a printingcylinder, the combination comprising, a leading edge clamp for engagingthe leading edge of the plate and positioning the same for peripheralregister, a trailing edge clamp having a hook for engaging the trailingedge of the plate, said hook being movable in said clamp, a Weightradially movable in said trailing edge clamp under the influence ofcentrifugal force, and means including a Wedge block on said hookWedgingly engaged by said weight and tending to urge the hook in a platetensioning direction, said wedging surfaces on said wedge block being soangled as to prevent retrograde movement of the hook so that the plateis maintained positively positioned at a constant peripheral dimensionwith the result that working of the plate on the cylinder is obviated.

3. In a tension lookup for use with a printing plate having grooves onthe underside thereof adjacent the leading and trailing edgesrespectively, the combination comprising, a leading edge clamp includinga hook for engaging the groove at the leading edge of the plate and forpositioning the same for peripheral register, a trailing edge clamphaving a hook for engaging the groove at the trailing edge of the plate,said hook having a pivoted finger for mounting the same for movement ina peripheral direction, relative to said groove, means for lightlybiasing the hook in a direction to clamp the plate in tension so as toeffect continuous follow-up of the hook against the groove uponelongation of the plate, said trailing edge clamp including a movableweight mounted to move radially outward under the action of centrifugalforce as the plate cylinder is rotated, and a wedge member coupled tosaid finger and engaged by said weight with the wedging surface soarranged as to be irreversible for locking the finger against retrogrademovement during rotation of the plate cylinder.

4. In a tension lookup for clamping a printing plate on a printingcylinder having a plurality of evenly spaced surface grooves around itsperiphery, the combination comprising leading edge clamps for engagingthe leading edge of the plate, said clamps being adjustable in saidsurface grooves to effect peripheral register, trailing edge clampshaving hooks for engaging the trailing edge of the plate, said hooksbeing movable in said trailing edge clamps, said trailing edge clampsbeing adjustable in said surface grooves to lookup the plate, respectiveweights radially movable in said trailing edge clamps under theinfluence of centrifugal force, and means including respective wedgingsurfaces between saidweights and said hooks for urging the hooks in aplate tensioning direction upon outward movement of the weights, theangle of said wedging surfaces being suiciently shallow to preventretrograde action.

5. In a tension lookup for clamping a printing plate on a printingcylinder, the combination comprising a plate tensioning hook forengaging an axially oriented edge of the plate; means carrying said hookfor circumferential movement, a Weight movable radially under theinfluence of centrifugal force, and means including a wedging surfacebetween said weight and said hook for urging the hook in a platetensioning direction upon outward movement of the weight, the angle ofsaid wedging surface being sufficiently shallow to prevent retrogradeaction.

Y HENRY L. MCWHORTER.

References Cited in the i'lle of this patent UNITED STATES PATENTSNumberv Name Date 891,857 Perry June 30, 1908 1,343,220 Mast June 15,1920 1,486,323 Claybourn Mar. 11, 1924 1,619,650 Brugmann Mar. 1, 19272,047,364 Foster July 14, 1936 2,050,950 Huck Aug. 11, 1936 2,236,230Worthington Mar. 25, 1941 2,406,883 Luehrs Sept. 3, 1946 2,413,174Crafts et al. Dec. 24, 1946 FOREIGN PATENTS Number Country Date 315,446Italy Feb. 26, 1934

